Myxo paramyxo viruses are being used as probes to evaluate the part played by lymphocytes in the induction and expression of cell-mediated immunity. The rationale is that individual viruses differ in their capacity to infect lymphocytes or cleave surface membrane structures that influence lymphocyte traffic patterns in the body. The plan is to further define classes of lymphocytes effected by Newcastle disease virus, Sendai virus and various influenza viruses. Another approach would involve selective deletion of defined lymphocyte subsets from rat thoracic duct lymph using affinity columns prepared by linking viruses or their proteins to an insoluble carrier. BIBLIOGRAPHIC REFERENCES: McGregor, D.D. and G.B. Mackaness. (1975). The properties of lymphocytes which carry immunologic memory of 0X 174.J. Immunology 114, 336. Kostiala, A.A.I. and D.D. McGregor (1975). The mediator of cellular immunity. XI The relationship between cellular hypersensitivity and cellular resistance in rats infected with Listeria monocytogenes. J. Exp. Med. 141, 1249.